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1 + (2 + 3 * 4) + (5 + 6 * 7 + 8 * 9 * 10) +....+ nth term

Jan 9th, 2017
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  1. // Problem: Get the sum of 1 + (2 + 3 * 4) + (5 + 6 * 7 + 8 * 9 * 10) + .... + nth term
  2.  
  3. /*
  4.  * while n = 10, sum is 782
  5.  * while n = 6, sum is 26
  6.  * while n = 19, sum is 10123
  7.  * while n = 2, sum is 3
  8.  */
  9.  
  10. #include <iostream>
  11. using namespace std;
  12.  
  13. int main() {
  14.     int n; cout << "Input: "; cin >> n; // getting nth term
  15.     int sum = 0, loop = 1 /*for first inner loop*/, num = 1 /*number initializtion*/;
  16.     bool run = true; // to run the outer loop
  17.  
  18.     while (run) {
  19.         int inner_sum = 0; // for taking the value of each closed bracket
  20.         for (int x = 1; x <= loop; x++) /*inner loop for the sum of bracket*/ {
  21.             int mult = 1;
  22.             for (int y = 1; y <= x; y++) /*inner loop for product*/ {
  23.                 mult *= num;
  24.                 if (num == n) { // if num crosses n then stop multiplying
  25.                     run = false;
  26.                     break;
  27.                 }
  28.                 num++; // number increment by 1
  29.             }
  30.             inner_sum += mult; // sum of each product of a bracket
  31.             if (num == n) // if num crosses n then stop next loop
  32.                 break;
  33.         }
  34.         sum += inner_sum; // sum of participated brackets
  35.         loop++; // increment of repeatation of inner loop
  36.     }
  37.     cout << "\nSum: " << sum << endl;
  38.     return 0;
  39. }
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